When I first started at Citrix, I did a lot of training with the XenServer Workload Balancing Architect Deane Smith. Deane has moved on from Citrix but his architecture remains and it’s one of the cleverest and most well thought out componentised examples of product design that I’ve seen.

XenServer Workload Balancing (WLB) is one of the most distracting examples of product naming I’ve seen. It sets the stage that this product is primarily about balancing workloads automatically which many administrators prefer to do themselves. Additionally licensing meant that it wasn’t always available so was often overlooked by XenApp and XenDesktop users.

The recent release of a new version of XenServer 6.5 and a new version of WLB adds more functionality, a better user interface, improved auditing functionality and changes in licensing that make it relevant to more users on the XenServer platform including those using Citrix XenDesktop, HDX and XenApp.

So what can WLB do for you?

XenServer WLB basically has 4 layers; the upper most being that bit of icing on the cake that is the ability to automate balancing of workloads; however the majority of its power and use cases lies in the underlying 3 layers.


Layer 1: Collection and archiving of XenServer metrics with fine granularity; Alert setting based on collected metrics;

  • XenCenter monitoring uses RRDs that decrease in granularity over time; WLB offers the user the option to retain metrics at controlled granularity – offers a free alternative to third party monitoring or Director for users with a license. An administrator can come in on Monday morning and see in fine granularity metrics associated with a crash on Friday. Or an administrator can review average usage over the year to identify spare capacity whilst retain the granularity to identify peak usage.

Layer 2: Historical Trend Analysis of metrics; Metric report generation; Chargeback capability

  • WLB allows system administrators to set alerts triggered by metric thresholds and the analysis layer
  • Reports allow auto-capacity planning by system administrators
  • Chargeback functionality

Layer 3: Alerts raised and VM positioning recommendations

  •  WLB alerts administrators based on both thresholds and historical trend data alerting users to resource problems in their deployment and also makes recommendations for VM migration to administrators

Layer 4: Automated Workload Balancing performed based on recommendations from layer 3

  • Administrators can configure a deployment to automatically respond to the recommendations and make corrective action to improve the performance on a deployment

I’ve always loved the architecture of this product and how every layer adds standalone value to a system administrator. It’s a product designed with the full understanding that system administrators are not just day to day caretakers needing pure administration functionality. System Administrators nowadays are in fact system capacity planning architects, manage budgets and staff, trouble shooters and provide key executive insight. WLB offers administrators an easy way to generate the reports finance and exec managements need easily, highlight infrastructure resource limitations, demonstrate when hardware is at capacity, identify the bottlenecks where resource investment is most needed as well as where there is spare capacity reducing TCO.

I think one of the reasons system administrators are so suspicious of automated load balancing is because a lot of the products aren’t robust enough and the recommendations primitive and often flaky. XenServer has had several years to get this right and I’ve seen the code, seen it in production – so this is one of the few load balancing products I actually recommend. So if you are a XenDesktop or XenApp administrator with WLB for the first time as a result of the new licensing model, have a look at this – go play!!!

In my next blog, I’m hoping to highlight a few use cases and gems in WLB, particularly suited for needs of HDX customers using XenApp and XenDesktop, so keep your eyes open. Update: New blog is out! Read it here!

In the meanwhile, find out about the power of WLB

XenServer WLB has a fascinating and very readable administrator guide, check it out here, packed full of real world examples. I strongly recommend reading this as you’ll find use cases that open your eyes to the power and possibilities for administrators. You just have to read the index to see the nuggets of joy for system administrators – with topics like (a tiny fraction below):

  • “3.2. Choosing the Best Host for a VM”
  • “3.3.2. Understanding WLB Recommendations under High Availability”
  • “ Chargeback Utilization Analysis”
  • “ Pool Optimization History”
  • “ Optimizing and Managing Power Automatically”
  • “ Designing Environments for Power Management and VM Consolidation”

Enterprise Ready

WLB is now a mature enterprise level feature of XenServer, with a long and proven history (best part of a decade of development). A large part of its development, over several years, was hardening the behaviour and recommendations when a system is under load. This product comes into its own when you network, servers and system are starting to struggle. It’s easy to make a monitoring product that works on a healthy system, when your network is failing and metric collection starts to fail writing a resilient product takes a lot of thought and testing, which is what you now have with WLB 6.5. WLB is, of course, designed to work with all those other enterprise level XenServer features such as High Availability and Dynamic Memory allocation.

WLB was retired for XS6.2 whilst an expanded team was established to revamp the underlying architecture, a lot of people thought it had gone away, development and enhancements were actually underway. This was part of a long term plan to ensure this product was future proof and hardened to align with the expanded scalability and demands of the now released and re-architected XenServer 6.5. I think this confused a lot of people as to why the product was temporarily unavailable, the engineering demands for a product sometimes aren’t that transparent and I think we didn’t message it well (one we’ve learned from). The enhanced architecture now positions WLB as well-suited to the scales seen in VDI with XenDesktop and XenApp as well as Cloud.

A Couple of Tips!

  • XenCenter ONLY shows out WLB tab for configuration when the XenServer pool is licensed (Enterprise or above license type), this indicates that if the WLB tab is hidden, the XenServer pool is NOT licensed. See the -WLB 6.5 Quick Start Guide (Section 1.3)
  • How to upgrade to WLB6.5 – see the WLB 6.5 Quick Start Guide and  please refer CTX141838

Further Information


These are quite large but I think seeing the detail available is useful!

Configure and weight threshold limits for CPU, RAM, network usage etc
Get an overview of your pool’s health
Drill down into your pool health history
Check out chargeback reports!